Before the discovery, the largest known groups of Irrawaddy dolphins amounted to a few hundred or fewer. The species is considered vulnerable by the International Union of Conservation of Nature; the decision to list it on the IUCN's Red List was made based upon declines in the known populations.

"This discovery gives us great hope that there is a future for Irrawaddy dolphins," said researcher Brian D. Smith of the Wildlife Conservation Society, who led the study. "Bangladesh clearly serves as an important sanctuary for Irrawaddy dolphins, and conservation in this region should be a top priority."

But Smith and other researchers cautioned that the Irrawaddy dolphin still faces many perils, among them rising sea levels caused by climate change and contact with human fishermen. During the study, researchers found two dolphins that had drowned after becoming tangled in fishing nets. Local fishermen acknowledged that this was a common occurrence.

The results of the study were made public Wednesday at the First International Conference on Marine Mammal Protected Areas in Maui, Hawaii. The news release did not say when the study was conducted but Bangladeshi researchers in the team said it was launched in 2004.

Ainun Nishat, the Bangladesh head of International Union for Conservation of Nature, said the finding was an indication that "ecology in the area is not dead yet."

"There is plenty of food, mainly fish, in the area for the dolphins to eat," said Nishat, who was not involved in the study. "What is now needed is to restrict fishing in the area to protect the dolphins."

The Wildlife Conservation Society has requested that Bangladeshi authorities establish a sanctuary in the Sundarbans for the dolphins. "The sanctuary may take time," Mohammad Jalilur Rahman of the Bangladesh Fisheries Research Institute told the Associated Press. "But we are already motivating the fishermen not to harm the dolphins which get entangled in their nets."

Irrawaddy dolphins are closely related to orcas and are native to
freshwater lagoons, rivers and estuaries in southeast Asia. They have
blunt, beakless faces that more closely resemble orca or beluga whales
than bottlenose dolphins.